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Lecture 11 - Descending Tracts - lecture

Lecture 11 - Descending Tracts - lecture - Higher Centers...

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Higher Centers of Motor Control
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Outline 1. Motor cortex (Primary, premotor & SMA) 2. Descending pathways a. Dorsolateral pathways b. Ventromedial pathways c. Brainstem reflexes 1. Clinical correlations a. UMN lesions b. Cerebral palsy
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Higher Centers of Motor Control Involved in voluntary movement Provide motor signals via long descending tracts from the cerebrum These tracts involve the cortex, the brainstem and the spinal cord. UMNs –< LMNs (alpha & gamma) UMNs –< interneurons Muscle tone, posture, reflexes and movement are all controlled by a balance of the long descending tracts Like the sensory systems, the motor tracts are a set of parallel pathways, with overlapping and complementary functions.
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Overview of Cerebral Cortex Covers the cerebral hemispheres and gives the brain its convoluted appearance; about 2.5 sq. ft Organized topographically (by sensory modality) and somatotopically (homunculus) Six cell layers thick (gray matter) Efferents from the cortex: must be connected with other cortical areas or with subcortical sites
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Motor Cortex Primary Motor Cortex Controls contralateral voluntary movements Especially the fine movements of the hands and face. Hand, foot, lower face are entirely contralateral. Muscles that tend to be active bilaterally simultaneously are controlled by M1 on both sides. Premotor Cortex Motor planning area Controls trunk & girdle muscles of the body Supplementary Motor Cortex Motor planning area Initiation of movement, orientation of eyes & head, planning bimanual and sequential movements All motor cortices above receive info from sensory association areas, BG & cerebellum
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Primary Motor Cortex Somatotopic organization Motor homunculus Has greater representation of hand & lower face, not rigidly fixed Receives info from thalamus
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Motor Somatosensory Degree of representation is proportional to the precision of movement required by that body part -Face and fingers have LARGE representation
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Descending Tracts Dorsolateral System Control limb flexion & fine movement 1. Lateral corticospinal tract 2. Rubrospinal tract 3. Lateral reticulospinal tract 4. Corticobulbar tract Ventromedial System Control of trunk & limb muscles 1. Anterior corticospinal tract 2. Medial reticulospinal tract 3. Medial vestibulospinal tract 4. Lateral vestibulospinal tract 5. Tectospinal tract
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Descending tracts from cortex:  Lateral corticospinal tract (Dorsolateral System) Huge tract: ~ 1 million axons Function Voluntary control of distal muscles needed for precise movement
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